FIG. 5 shows an essential part of a conventional one-way clutch in a sectional view by way of example. Referring to FIG. 5, a conventional one-way clutch 001 includes an inner race 002 rotated by external power, an outer race 003 surrounding the inner race 002 to transmit power to a driven member and provided with pockets 004, rollers 0005 placed in the pockets 004, and springs 006 pressing the rollers 005 in a specific direction.
In the following description, a direction in which the springs push the rollers is referred to as “forward direction”. The bottom surfaces 004a, i.e., surfaces on the side of the outer circumference of the outer race among the surfaces of the pockets 004, are curved such that the depth of the pockets is smaller at the forward ends of the pockets 004. Thus, taper spaces tapering in a direction in which the springs 006 push the rollers are formed between the bottom surfaces 004a and the outer circumference of the inner race 002. While the one-way clutch is at a stand still, the rollers 005 pressed against the outer circumference of the inner race 002 and the bottom surfaces of the pockets 004 and held stationary in substantially middle parts of the pockets 004 by the springs 006. Stopping positions where the rollers are held stationary in the substantially middle parts of the pockets will be referred to as “standard roller-stopping positions” in the following description.
The rollers 005 jam into the forward tapered space formed between the outer circumference of the inner race 002 and the bottom surfaces 004a of the pockets 004 when the inner race 002 rotates in the direction of the arrow W. Consequently, power is transmitted from the inner race 002 to the outer race 003 to rotate the outer race 003 in the direction of rotation of the inner race 002. A driven member is fastened to the outer race 003 by screwing bolts, not shown, in threaded holes 003a formed in the outer race 003. Thus, the driven member is rotated by the power transmitted to the outer race 003. When the inner race 002 rotates in a direction opposite to the direction of the arrow W relative to the outer race 003, the rollers 005 are released and power is not transmitted.
Generally, the three rollers 005 are arranged at equal center angular intervals (angular intervals about the center axis) so that the rollers 005 are evenly in contact with the inner race. When the one-way clutch is loaded with a large load, the number of the rollers is doubled. The number of the pockets 004 is equal to that of the rollers. Similarly, the number of the threaded holes 003a is three to attach the driven member to the outer race stably. The threaded holes 003a are at equal distances from the center of the outer race and are arranged at equal center angular intervals. The one-way clutch shown in FIG. 5 is provided with the six rollers, the six pockets and the three threaded holes.
Buffer clearances are secured in front of the rollers 005 in the pockets 004 defining the forward tapered spaces to absorb dimensional errors in the bottom surfaces of the pockets 004 and the outer circumference of the inner race. Therefore, the rollers 005 never come into contact with the front end surfaces 004b of the pockets.
The positional relation between the standard roller-stopping position and the pocket 004 is the same for all the pockets. The center angular intervals between the adjacent pockets 004 are equal to the center angular intervals between the adjacent standard roller-stopping positions. In the conventional one-way clutch, the center angular intervals between the adjacent ones of the six pockets are 60°, and the center angular intervals between the adjacent ones of the three threaded holes 003a are 120°.
In a one-way clutch of a certain nominal size provided with pockets arranged at equal center angular intervals, the distance d between the threaded hole 003a and the corresponding pocket 004 was 2 mm. The distance d seemed to be excessively small in view of the rigidity of the outer race and it was considered that the distance must be somewhat greater than 2 mm.
To increase the capacity of the one-way clutch, the outside diameter of the inner race must be increased, and the rollers must be shifted radially outward accordingly. If the outside diameter of the outer race 003 is increased and the threaded holes 003a are shifted radially outward, the size of a device provided with the one-way clutch increases, which is undesirable. If the threaded holes 003a formed in the outer race 003 provided with the plurality of pockets are not shifted radially outward, the distance d between the threaded holes 003a and the corresponding front end surfaces 004b is reduced, which reduces the rigidity and is undesirable.
The present invention is intended to provide means for securing a sufficiently long distance between the threaded holes and the corresponding front end surfaces of the pockets in a one-way clutch including an outer race provided with a plurality of pockets, to prevent the reduction in strength of the outer race without enlarging the outer race and to achieve space saving.
On the other hand, the conventional one-way clutch required highly accurate work, which includes fabrication of high-precision spring caps having a highly precise outer diameter and machining of an insertion hole having a highly precise inner diameter to ensure smooth sliding movement of the spring cap within the insertion hole. This highly accurate work inevitably increased the manufacturing costs and man-hour requirements. Further, in the case where a large number of pockets are formed in the outer race, the outer diameter of the outer race had to be increased to avoid close arrangement of the insertion holes and the pockets.